At present, various types of device are known for fractioning a blood sample into multiple aliquots and for mixing them with reagents suitable for these various different analyses that are to be performed.
Firstly, sampling valves are known, e.g. such as those taught by French patent application FR 2 622 692 in the name of the Applicant.
Such sampling valves enable automatic analyzers to operate at a high rate and they are conventionally used only in top-of-range appliances since such valves are expensive to fabricate and to adjust.
Furthermore, sampling valves present the drawback of requiring regular and complex maintenance, thus making them more expensive to operate. Also, sampling valves present the drawback of requiring volumes of blood that are greater than the volumes theoretically necessary for performing analyses.
Other systems have been developed for fractioning a sample of blood. By way of example, mention may be made of documents U.S. Pat. No. 5,254,313 or EP 0 543 544 filed in the name of TOA Medical. In both those documents, the blood sample is taken from an open tube, and there is no system for piercing a tube stopper. The blood fractions (or aliquots) are mixed with the reagent(s) in one or more mixing vessels. Finally, it is a moving portion of the valve that enables aliquoting.
Mention may also be made of patent WO 2005/010488 filed by Dade Behring, in which samples can be taken from a tube that is closed by a stopper. However in that document also, the mixing of the sample with the reagent takes place in a mixing vessel. In addition, the sample-taker needle needs to be moved horizontally over the mixing vessel.
Another type of system is also known for fractioning a blood sample into multiple aliquots, and is described in patent application EP 0 913 680 A1 in the name of the Applicant.
The device described in that document has a sample-taker member made up of a first striker tube for piercing a tube from which a sample of blood is to be taken, and for admitting air into the tube, and a needle mounted coaxially inside the striker to take the sample of blood from the tube and then dispense various aliquots from the sample taken from the tube into respective streams of reagent within different analysis vessels. The sample-taker member of the system is connected to a syringe for sucking up a determined volume of blood from the tube of blood for analysis, and then for dispensing the aliquots mixed with the appropriate reagents into the various analysis vessels. Said sample-taker member is mounted on a device that is movable in translation both vertically and horizontally by motor-driven means in order to be capable of entering into tubes of blood to take the samples of blood for analysis therefrom, and then dispense respective aliquots of blood into each of the measurement vessels. The system thus enables multiple aliquots to be dispensed from a single sample of blood in very accurate manner without the above-described drawbacks of sampling valves.
Nevertheless, the fractioned dispensing system described in EP 0 913 680 A1 is not entirely satisfactory either.
The multiple movements of the sample-taker member firstly for taking the sample of blood from the tube and subsequently for dispensing the various aliquots of said sample into the analysis vessels require the mechanical systems that move the sample-taker member to be adjusted accurately. It is also possible to observe a certain amount of variation over time in the accuracy with which the sample-taker member is positioned when dispensing blood aliquots into the analysis vessels relative to the orifices for introducing reagents into said vessels.
Furthermore, under certain very particular conditions, the sample-taker member of the system with a coaxial striker and sample-taker needle can suffer from dirtying as a result of successive piercing operations of the same tube, so that small pieces of stopper or of dried blood can become engaged between the needle and the inside body of the striker, thereby disturbing the preparation of aliquots.